Generally, in electrostatographic reproduction, the original to be copied is rendered in the form of a latent electrostatic image on a photosensitive member. This latent image is made visible by the application of electrically charged toner.
The toner forming the image is transferred to a substrate also referred to in the art as a receiver such as paper or transparent film, and fixed or fused to the substrate. When heat softenable toners, for example thermoplastic polymeric binders, are employed, the usual method of fixing the toner to the substrate involves applying heat to the toner, once it is on the substrate surface, to soften it, and then allowing the toner to cool. This application of heat in the fusing process is preferably at a temperature of about 90° C.-220° C. Pressure may be employed in conjunction with the heat. Various additives and oils are used to aid the transfer of the particles. Silicone oil is commonly used as a release oil because it is thermally stable and incompatible with the toner particles and other polymers in the printer.
A system or assembly for providing the requisite heat and pressure is generally provided as a fusing subsystem, and customarily includes a fuser member and a support member. The various members that comprise the fusing subsystem are considered to be fusing members; of these, the fuser member is the particular member that contacts the toner to be fused by the fusing subsystem. Heat energy employed in the fusing process is transmitted to the toner on the substrate by the fuser member. Specifically, the fuser member is heated; to transfer heat energy to the toner situated on a surface of the substrate, the fuser member contacts this toner, and also can contact this surface of the substrate itself. The support member contacts an opposing surface of the substrate.
Accordingly, the substrate can be situated or positioned between the fuser and support members, so that these members can act together on the substrate to provide the requisite pressure in the fusing process. Preferably, the fuser and support members define a nip, or contact arc, through which the substrate is passed. As a matter of preference, the fuser and support members are in the form of fuser and pressure rollers, respectively. One or both of the fuser and support members have a soft layer that increases the nip, to effect better transfer of heat to fuse the toner.
During the fusing process toner can be offset from the substrate to the fuser member. Toner transferred to the fuser member in turn may be passed on to other members in the electrostatographic apparatus, or to subsequent substrates subjected to fusing. Toner on the fusing member can interfere with the operation of the electrostatographic apparatus and with the quality of the ultimate product of the electrostatographic process. This offset toner is regarded as contamination of the fuser member, and preventing or at least minimizing this contamination is a desirable objective.
Toner offset is a particular problem when polyester toners are used. Polyester toners are frequently used in high quality color and black and white printing applications. In particular, offset to the fuser member can collect on other members of the fusing subsystem, such as external heating members for heating fuser members, and release agent applicators e.g., oilers. In this regard, release agents can be applied to fusing members during the fusing process, to prevent or minimize toner offset. These agents usually are or include polyorganosiloxanes, particularly polyorganosiloxane oils. The polysiloxanes have anti-adhesive properties that are favorable for protecting the surface of the fuser member, and maintaining the durability of the fuser member.
Modified polysiloxanes having functional groups provide a protective barrier by attaching to the fuser surface via specific interactions between the functional groups and the fuser surface. The interaction of the functional groups with the fuser surface allows the polysiloxane to sterically block contact of the toner with the fuser member surface and provide a protective barrier. Mono-functional polysiloxanes with one reactive functional group may interact with the fuser member or toner surface to provide a protective coating as well as increase the wetting of nonfunctional components in the polymeric release agent composition. Multifunctional polysiloxanes with more than one reactive group also interact in the same manner to provide a protective coating; however, the presence of more than one functional group may allow undesired additional interaction with other components.
As to functional poly-organosiloxanes, U.S. Pat. No. 6,261,688 and U.S. Publication No. 2001/0019768 disclose polymeric release agents comprising organosiloxane polymers with tertiary amino functional groups. Among the tertiary amino functional groups disclosed are those where the N atom has an alkyl or arylalkyl as one substituent group, and an acyl [—C(═O)—CH3] group as the other. U.S. Pat. No. 5,157,445 discloses a toner release oil composition containing an organopolysiloxane with one or more secondary amino substituents, where the secondary amine N atom has a C1-8 alkylene substituent terminated by NH2. Also disclosed as eligible release oil ingredients are organopolysiloxanes having aromatic secondary amino substituents.
U.S. Pat. Nos. 5,531,813 and 5,512,409 disclose secondary amino functional polyorganosiloxanes, where the N atom can have, besides the H atom, a C1-18 alkyl or arylalkyl substituent. These patents also disclose the polyorganosiloxanes as monoamino functional polymers, with the monoamino functionality interacting with the hydro-fluoroelastomer surface of a fuser member; this interaction is stated to provide a barrier to the toner, as well as a low surface energy film to release the toner from the surface. Additionally as to monoamino functionality in particular, branched T-type monoamino functional poly-siloxanes, in which the reactive group is attached to a central silicon atom, are disclosed in U.S. Pat. No. 5,516,361.
Functional polysiloxanes are described in U.S. Pat. No. 4,101,686, which discloses polymeric release agents having functional groups such as carboxyl, hydroxy, epoxy, amino, isocyanate, thioether, and mercapto groups. This patent states that the polymeric release agents are applied to a heated fuser member to prevent toner adhesion. Similarly, U.S. Pat. Nos. 4,272,179 and 4,264,181 disclose polymeric release agents which have functional groups, and which are applied to the surface of a fuser member.
Additionally, U.S. Pat. Nos. 5,141,788 and 5,281,506 disclose a fuser member comprising a polyorganosiloxane having reactive functional groups that are grafted to the surface of the cured fluoroelastomer layer. U.S. Pat. No. 4,853,737 discloses a fuser roller having an outer layer comprising a cured fluoroelastomer, with polydiorganosiloxane segments that are covalently bonded to the backbone of the fluoroelastomer; the polydiorganosiloxanes have functional groups, at least one of which is present on the polydiorganosiloxane chain to form the covalent bond to the fluoroelastomer backbone.
U.S. Pat. No. 7,074,488 discloses mono-functional branched polysiloxanes, wherein the branched siloxane chain provides enhanced coverage of the surface and resistance to extension under shear. This provisional application is incorporated herein in its entirety, by reference thereto.
In addition to functional groups, polysiloxane release fluids have been modified with non-reactive organo groups that promote interaction or wetting of surface components. U.S. Pat. No. 5,780,545 discloses a stabilized polyether modified organosiloxane that acts as a surfactant to promote wetting and that reduces offset. U.S. Pat. Nos. 5,568,239, 5,641,603, 5,627,000, and 5,636,012 disclose polyorganosiloxanes modified with side groups or end groups of fluorocarbon chains, for promoting the wetting of fluorocarbon surfaces such as tetrafluoroethylene. U.S. Pat. Nos. 5,783,719 and 5,959,056 disclose long chain hydrocarbon modification of organosiloxanes as solid release agents, and as being useful for other purposes e.g., sealing toner cartridges; further, it is suggested that the long hydrocarbon chain may also act as a surfactant for the toner.
U.S. Pat. Nos. 7,208,258; 7,214,462; 7,198,875; 7,186,462 and U.S. Patent Application US 2005/0287372 to Xerox states that the level of multifunctional aminosiloxane in the release fluid is related to the amount of gel formed on the fuser roller. This in turn affects toner offset to the fuser roller and print quality defects. These patents teach techniques to control the level of functionality of the siloxane, to make amino-siloxanes where the functional group is internal or pendant to the polymer backbone. The functional groups are located along internal parts of the polymer chain but are not solely at the end of the chains.
It would be desirable to have an agent that promotes wetting as a surfactant, and that also exhibits reactivity to and/or interaction with polar sites—on the toner, or on the fuser member surface to act against or combat adherence of the toner to surfaces, or to polar sites on fuser members, that tend to attract toner offset. It would further be desirable that the composition could be easily prepared. It would yet additionally be desirable that the composition have labile hydrogen for reacting to surfaces.